why would you use a bar graph
Histograms and bar graphs look very similar. What's different about them? Let's take a look at an example of each. Here's a bar graph. What do you notice about it? Well, the bars represent different categories. Exactly! Could we rearrange the bars if we wanted? For example, could we move "Debt Interest"
to go after "Social Programs" but before "Social Security Medicare"? I think so. It doesn't look like the order matters at all as long as the billions of dollars
still matches every category. That's right! Let's take a look at a histogram now and tell me what you notice. The bars don't really represent different categories anymore. Or if they do, they're not as
clearly labeled. You're right! They don't represent different categories. Can you tell what they do represent? It says "average SAT math score". I would think that the height of the bars represents the
number of people who got that score. So then the different bars show how many students got
each score, right? Is that what the histogram says? Every student who gets a 500 is put into one bar, and every
student who gets a 510 is put in another bar? No, there aren't enough bars for that.
Then how do they decide which scores go into which bars? It looks like they use ranges, but I'm not sure how they know what range to use. That's exactly right! Histograms use continuous data where the bins represent ranges of data
rather than categories. Can you rearrange the bars in a histogram like you could in a bar
graph? No, that would be too confusing. Exactly! Now let's think about different sets of data and which would be better a histogram
or a bar graph. For instance, let's suppose we want to compare total revenues of five
different companies. Would you use a histogram or a bar graph? I would think you'd use a bar graph where each company is a different category and gets its
own bar to show total revenue. That's right! What about another example: We have measured revenues of several companies. We
want to compare numbers of companies that make from 0 to 10,000; from 10,000 to 20,000; from
20,000 to 30,000 and so on. Those are ranges of data so that sounds like a histogram. Exactly! Now what if we were looking at answers from a test question where students had four
choices: 4, 5, 6, and 7. We want to compare how many students chose each answer.
bar graph? Well, they're a series of numbers just like the SAT scores so I would choose a histogram. Suppose that the answers to a test question were the following: rabbit, horse, dog, elephant. Which would you choose then? Bar graph because they're different categories. That's right. In the case of the answers 4, 5, 6, and 7, you would do the same thing. These
are categories, even if the category labels are also numbers. They're not ranges like you need
for a histogram. I think I get it now. Even if there are numbers, you have to ask whether or not they're
ranges or categories. Exactly! I think you're ready to start working with histograms and bar graphs now!
What is the difference between a bar graph and a histogram? Hi, There are two differences, one is in the type of data that is presented and the other in the way they are drawn. In bar graphs are usually used to display "categorical data", that is data that fits into categories. For example suppose that I offered to buy donuts for six people and three said they wanted chocolate covered, 2 said plain and one said with icing sugar.
I would present this in a bar garph as: Histograms on the other hand are usually used to present "continuous data", that is data that represents measured quantity where, at least in theory, the numbers can take on any value in a certain range. A good example is weight. If you measure the weights of a group of adults you might get and numbers between say 90 pounds and 240 pounds. We usually report our weights as pounds or to the nearest half pound but we might do so to the nearest tenth of a pound or however acurate the scale is. The data would then be collected into categories to present a histogram. For example: might be a histogram for heights (with the appropriate scale on the vertical axis). Here the data has been collected into categories of width 30 pounds. The difference in the way that bar graphs and histograms are drawn is that the bars in bar graphs are usually separated where in histograms the bars are adjacent to each other. This is not always true however. Sometimes you see bar graphs with no spaces between the bars but histograms are never drawn with spaces between the bars. I hope this helps,
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